1,721,098 research outputs found
Numerical schemes for hyperbolic systems of conservation laws with stiff diffusive relaxation
No full textHyperbolic systems of conservation laws often have diffusive relaxation terms that lead to a small relaxation limit governed by reduced systems of a parabolic or hyperbolic type. In such systems the understanding of basic wave pattern is difficult to achieve, and standard high resolution methods fail to describe the right asymptotic behavior unless the small relaxation rate is numerically resolved. We develop high resolution underresolved numerical schemes that possess the discrete analogue of the continuous asymptotic limit, which are thus able to approximate the equilibrium system with high order accuracy even if the limiting equations may change type
A convergent adaptive wavelet-Rothe method for elastoplastic hardening
No full textTheme Issue "Wavelet and Fractal Methods in Science and Engineering
On design and analysis of a drivetrain test rig for wind turbine health monitoring
No full textThe reliability of offshore wind turbines is a key factor when estimating maintanence costs, downtime due to component failure and overall efficiency during operational life. Offshore wind turbines have limited accessibility and operate in harsh environments and, as a result, it is difficult to perform frequent checks on electrical and mechanical component. Drivetrain test rigs (DTR) are crucial to the task of: Validating the design of new components to avoid early life failure, observe the behaviour of components under load over long periods of time in a controlled environment and produce a maintanence plan that minimize costs and frequency of intervention. In this paper, after a brief introduction on the state of the art in DTR technology, is described a methodology that can be used to create an effective conceptual design for a drivetrain test rig, focusing also on the possible downscaling. The paper starts by analyzing the benefits of the drivetrain use in the wind power industry, bringing examples of real test rigs used in industrial and academical world. Once the topic is mastered it is possible to proceed with a description of the various phases needed to obtain the conceptual design, from the definition of layout to the preliminary 3D modeling. The test rig that is here designed, while inspired from full scale dynamometers used in the industry, is thought as a laboratory tool for academical use that can be used by students to investigate fault detection methods and health monitoring systems of wind turbines. It is also included a section dedicated to the possible techniques for downscaling the test rig, based on simple considerations of the drivetrain mechanical behaviour. Downscaling becomes a key factor when facing the need to test turbine components of ever increasing dimensions in laboratories with limited space and budget. The definition of a procedure to create a scaled version will allow laboratories to build test rigs of smaller dimension but with a damage model for the various components still closely linked to the one in real scale. Downscaling is also a necessity when working with limited power sources, not able to recreate the conditions that the real scale turbine encounters. The ultimate goal is to define a solid base to allow further development in the detailed design phase
Spectral methods for one-dimensional kinetic models of granular flows and numerical quasi elastic limit
No full textIn this paper we introduce numerical schemes for a one-dimensional kinetic model of the
Boltzmann equation with dissipative collisions and variable coefficient of restitution. In particular,
we study the numerical passage of the Boltzmann equation with singular kernel to nonlinear friction
equations in the so-called quasi elastic limit. To this aim we introduce a Fourier spectral method for
the Boltzmann equation [25,26] and show that the kernel modes that define the spectral method have
the correct quasi elastic limit providing a consistent spectral method for the limiting nonlinear friction
equation
Numerical Schemes for Kinetic Equations in Diffusive Regimes
No full textThe diffusive scaling of many finite-velocity kinetic models leads to a small-relaxation time behavior governed by reduced systems which are parabolic in nature. Here we demonstrate that standard numerical methods for hyperbolic conservation laws with stiff relaxation fail to capture the right asymptotic behavior. We show how to design numerical schemes for the study of the diffusive limit that possess the discrete analogue of the continuous asymptotic limit. Numerical results for a model of relaxing heat flow and for a model of nonlinear diffusion are presented. 1 Introduction In the kinetic theory of rarefied gases, two-velocity models of the discrete Boltzmann equation describe the behavior of a fictitious gas of two kind of particles that move parallel to the x\Gammaaxis with constant and equal speed. So we can consider at time t the particles with a density u(x; t), which move in the positive x\Gammadirection, and the particles which move in the negative x\Gammadirection with a ..
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